Composite structure for electronic microsystems and method for production of said composite structure

ABSTRACT

The invention relates to a composite structure for electronic Microsystems and a method for producing this composite structure, with the composite structure being provided with a polycrystalline diamond layer ( 4 ) for heat withdrawal. The growth substrate ( 1 ) contains or forms a component layer ( 2 ) with the electronic Microsystems, which are provided with binary or higher order component compound semiconductors. A protective layer ( 3 ), which encloses the component layer at least indirectly almost entirely, is placed between the component layer  2  and the diamond layer ( 4 ). A material is selected for the protective layer whose reactivity with the precursor materials present in the deposition of the diamond layer ( 4 ) by means of CVD, preferably by means of plasma CVD, is smaller than that of the component layer ( 2 ), and said protective layer. In order for the protective layer ( 3 ) to develop sufficient effectivity, it must be applied with an original thickness of at least 20 nm, preferably at least 50 nm and particularly preferred at least 100 nm.

[0001] The present invention relates to a composite structure for electronic systems and a method for production of this composite structure as they both are described in the generic printed publication DE 197 18 618 C2 on which the present invention is based.

[0002] DE 197 18 618 C2 describes a composite structure in which microelectronic components, such as transistors, diodes, resistors, capacitors, inductive resistors, etc., or circuits made thereof, such as amplifiers, sensors, emission cathodes for electrons, etc., placed on a growth substrate of monocrystalline silicon are provided with a diamond thermoconductive layer. The printed publication also discloses a corresponding plasma CVD for applying the diamond layer. The thermoconductive layer is made of diamond, among other things, because this material also possesses good thermoconductivity despite electric insulation. Such a type of thermoconductive layer made, in particular, of polycrystalline diamond is, therefore, excellently suited for thermal management of microelectronic components.

[0003] However, depositing the diamond layer on the components must occur at, for epitaxial growth, low temperatures in order not to impair or even destroy the components.

[0004] Furthermore, despite the thermal expansion differing from that of the coated materials, adhesion of the diamond layer to the coated surface has to be good. Due to these conditions, the epitaxial growth of aforementioned diamond thermoconductive layer must be conducted with great care.

[0005] With, in particular, growth substrates and/or components provided with binary, ternary, quarternary or even higher grade compound semiconductors, there is the problem that these materials react very strongly with the hydrogenous plasma during application of the diamond, thereby destroying and/or even completely removing these materials.

[0006] EP 0681 314 A2 describes the production of a composite structure in which a crystalline-arranged, i.e. heteroepitactic in relation to the substrate, diamond layer is deposited on a suited monocrystaline growth substrate, e.g. of Si or GaAs, by means of an intermediate layer with a continues lattice structure. The goal is a structurally high grade diamond layer that is suited for production of electronic components on a diamond base. The purpose of the substrate is to permit oriented diamond growth and therefore the substrate contains no electronic components. A lattice constant similar as closely as possible to that of the diamond is required for this growth. Lattice mismatching should be reduced by employing a monocrystalline intermediate layer with lattice constants that lie between the lattice constants of the diamond and that of the substrate.

[0007] The object of the present invention is to develop a composite structure for microelectronic components and a method to produce this composite structure, which at least largely has the already mentioned advantages of a diamond thermoconductive layer.

[0008] This object is solved according to the present invention with a composite structure with the features of claims 8 respectively with a method with the method steps of claim 1. Due to the invented application and CVD deposition in sufficient thickness of the substances defined by their chemical reactivity in claim 1 and claim 2, the components of the hydrogenous plasma no longer reach the compound semiconductors of the component layer.

[0009] The component layer of the present composite structure contains electronic Microsystems such as for example ICs, semiconductor lasers, sensors, transistors, diodes etc. and/or components such as amplifiers, sensors, emission cathodes for electrons, etc. made thereof.

[0010] Expediently, metallic function layers such as strip conductors, etc., which should at least partially not be covered by the diamond layer, are also provided with a protective layer.

[0011] Depending on the application respectively based on the background of the to-be-protected materials, nitrides and/or oxides and/or carbides and/or oxynitrides and/or diamond-like carbon, especially silicon nitride, preferably Si₃Ni₄ and/or silicon oxide, preferably SiO₂, and/or silicon carbide, preferably SiC, and/or silicon oxynitrides have proven to be suited as materials for the protective layer. Moreover, aluminum nitride, preferably AlN, and/or aluminum oxide, preferably Al₂O₃, are also suited. The protective layer may be monocrystalline, polycrystalline (e.g. not of stoichiometric Si-nitride) or also amorphous (e.g. of diamond-like carbon).

[0012] In order to ensure with certainty the function of the protective layer, its layer thickness is selected in such a manner that it remains connected in a continuous, uninterrupted manner during the entire deposition process of the diamond layer. This applies especially in the case of self-consumption by the components of the plasma, in which the protective layer, although with reduced layer thickness, should nonetheless remain connected in a continuous, uninterrupted manner: i.e. the protective layer must enclose the pertinent materials at least until a continuous, uninterrupted diamond layer has been deposited. Despite the arrangement of such types of protective layers which, due to their low thermoconductivity, may negatively influence withdrawing heat from the diamond layer, heat withdrawal in the invented composite structures is still sufficient due to the remaining reduced thickness of the protective layers following deposition of the diamond layer.

[0013] The quality of the layer system composed of the diamond layer and the intermediate layer placed on the component layer for heat withdrawal is given by the quality factor. The quality factor of the thermal measure corresponds to the relationship between the temperature rise without the thermal measure, i.e. without the layer system, to the temperature rise with the layer system. Temperature rise refers to the difference between the peak temperature reached in the component layer during designated operation of the electronic components and circuits integrated therein and the ambient temperature. In the present method, the thickness of the diamond layer and the thickness of the intermediate layer are preferably measured in such a manner that the finished composite structure has a quality of 1.5 or more. This quality factor depends, among other things, on the thickness of the intermediate layer. With a given thickness of the diamond layer, the thickness of the intermediate layer must be designed during deposition in such a manner that the above condition is fulfilled, i.e. the intermediate layer should not exceed a certain thickness in the finished composite structure. This maximum thickness depends on the thermoconductivity of the intermediate layer. If poorly thermoconductive silicon nitride is employed as the intermediate layer, its thickness should not be more than 20 nm. With AlN as the intermediate layer, 200 nm is tolerable.

[0014] Ideally, the thickness of the intermediate layer is selected prior to applying the diamond layer in such a manner that it is, in particular in the case of poor thermoconductivity, only a few atom layers thick after application of the diamond layer.

[0015] Further useful embodiments of the invention are set forth in the corresponding subclaims. Moreover, the invention is made more apparent using the preferred embodiments depicted in the accompanying figures.

[0016]FIG. 1 shows a 100-fold magnification of a broken edge of an uncoated InP growth substrate;

[0017]FIG. 2 shows a 10,000-fold magnification of an InP growth substrate provided with a protective layer and a diamond layer;

[0018]FIG. 3 shows a 20,000-fold magnification of the surface of the composite structure according to FIG. 2:

[0019]FIG. 4 shows a 20,000-fold magnification of a GaAs growth substrate provided with a protective layer and a diamond layer;

[0020]FIG. 5 a 20,000-fold magnification of the surface of the composite structure according to FIG. 4; and

[0021]FIG. 6 schematic single steps of the method for producing the present composite structure.

[0022]FIG. 1 shows a 100-fold magnification of a broken edge of an uncoated InP growth substrate that was exposed to the process conditions for only a few seconds like those occurring during deposition of diamond by means of a BIAS-aided plasma CVD. It is quite evident that the InP growth substrate has been badly impaired. Corresponding tests have shown that an InP substrate of conventional layer thickness is etched completely through within only a few minutes.

[0023]FIG. 2 shows a 10,000-fold magnified broken edge of a coated InP growth substrate 1 that was coated first with a protective layer Si₃N₄ 3, then with the polycrystalline diamond layer 4. This test revealed that the layer thickness of the protective layer 3 should be at least 20 nm before deposition of the diamond layer, preferably at least 50 nm and particularly preferred at least 100 m.

[0024]FIG. 3 shows a 1:20,000-fold magnification of the diamond surface of the composite structure according to claim 2. This figure shows the polycrystalline character of the diamond layer particularly distinctly.

[0025]FIG. 4 shows a 20,000-fold magnification of a broken edge of a coated GaAs growth substrate 1. The GaAs growth substrate 1 was first coated with a protective layer 3 of Si₃N₄ and then with the polycrystalline diamond layer 4. It was again revealed that the layer thickness of the protective layer 3 should be at least 20 nm before commencing deposition of the diamond layer 4, preferably at least 50 nm and particularly preferred at least 100 m.

[0026]FIG. 5 shows a 1:20,000-fold magnification of the diamond surface of the composite structure according to FIG. 4.

[0027] This figure, too, shows the polycrystalline character of the diamond layer particularly distinctly.

[0028] The protective layer and the diamond layer were each produced by means of a prior art EIAS-aided plasma CVD process. The parameters used in the process are listed in the following table. DC power 2.7 kW Substrate temp. 180-360° C. Pressure 10.0-14.6 slm Gas flow 0.5 mbar Carbon sources CH₄, C₂H₄ Ratio C/H 0.15-0.3% Ratio O/C 30-100%

[0029] Details concerning a method of depositing a diamond layer can be found, for example, in the publication by M. Seelmann-Eggebert et al., “Heat-Spreading Diamond Films for GaN-based High-Power Transistor Devices”, Diamond and Related Materials 10, 2001, pp. 744-749. The content of its disclosure is included in the present summary of the invention.

[0030]FIG. 6 shows schematically single steps of the method for producing the present composite structure. First a growth substrate 1 provided with a component layer with electronic Microsystems is provided for (FIG. 6a). The component layer 2 can be made of, for example, GaN, the growth substrate of sapphire. In the next step, a protective layer 3 of Si₃N₄ is applied onto the component layer 2, with layer 3 enclosing the component layer 2 entirely (FIG. 6b). The magnified detail on the right shows as an example a component 6 of this component layer 2 with the respective connection metallization 5. Then a polycrystalline diamond layer is deposited on the protective layer 3 by means of plasma CVD. During the first period of this deposition, still before there is a thin, full-surface diamond layer, the protective layer 3 is attacked by the plasma during application of the diamond and, if need be, reduced in thickness. After a thin, full-surface diamond layer has been deposited, reduction stops (FIG. 6c), which is depicted exaggeratedly in the figure. The diamond layer deposition process continues until the desired layer thickness has been attained (FIG. 6d).

[0031] Using a mask, for example with the aid of a structured photoresist, during the diamond deposition ensures that the diamond layer does not cover the connection metallization 5 regions. The protective layer 3 is then removed from these regions so that they are accessible for external contacting (cf. magnified detail of FIG. 6d). 

What is claimed is:
 1. A method for producing a composite structure for electronic Microsystems, in which a growth substrate (1), which contains a component layer (2) with said electronic Microsystems, is provided for said composite structure, with said component layer (2) containing binary or higher order compound semiconductors; a protective layer (3), which encloses said component layer (2) at least indirectly completely, is applied onto said component layer (2); and a polycrystalline diamond layer (4) for heat withdrawal is applied onto said protective layer (3) by means of CVD, preferably by means of plasma CVD; with a material being selected for said protective layer (3), whose chemical reactivity with the precursor materials present in the deposition of said diamond layer (4) by means of CVD, preferably by means of plasma CVD, is lower than that of the component layer (2), and said protective layer (3) is applied with an original layer thickness of at least 20 nm, preferably at least 50 nm and particularly preferred at least 100 nm.
 2. A method according to claim 1, wherein nitrides and/or oxides and/or carbides and/or oxynitrides and/or diamond-like carbon are selected for said protective layer (3).
 3. A method according to claim 1, wherein, silicon nitride, preferably Si₃N₄, and/or silicon oxide, preferably SiO₂, and/or silicon carbide, preferably SiC, and/or silicon oxynitrides are selected for said protective layer (3).
 4. A method according to claim 1, wherein aluminum nitride, preferably AlN, and/or aluminum oxide, preferably Al₂O₃ are selected for said protective layer (3).
 5. A method according to claim 1, wherein at least a plurality of metallic function layers, in particular strip conductors are at least disposed regionwise within said diamond layer (4) and/or at least covered regionwise thereby.
 6. A method according to one of the claims 1 to 5, wherein all the surface regions of said component layer (2) which come into contact with the precursor material of said diamond layer (4) are covered with said protective layer (3).
 7. A method according to one of the claims 1 to 6, wherein the layer thickness of said protective layer (3) is selected in such a manner that after application of said diamond layer (4) it has a value with which a thermal quality factor of said diamond and protective layer (3,4) of 1.5 or more is yielded.
 8. A composite structure for electronic Microsystems, comprising a growth substrate (1), which contains a component layer (2) with said electronic microsytems, and a polycrystalline diamond layer (4) for withdrawal of heat, wherein said component layer (2) contains binary or higher order compound semiconductors, a protective layer (3), which encloses said component layer (2) at least indirectly completely, is disposed between said component layer (2) and said diamond layer (4), and the chemical reactivity of said protective layer (3) with the precursor materials present during deposition of the diamond layer (4) by means of CVD, preferably plasma CVD, is lower than the corresponding chemical reactivity of said component layer (2).
 9. A composite structure according to claim 8, wherein said protective layer (3) comprises nitrides and/or oxides and/or carbides and/or oxynitrides and/or diamond-like carbon.
 10. A composite structure according to claim 8, wherein, said protective layer (3) comprises silicon nitride, preferably Si₃N₄, and/or silicon oxide, preferably SiO₂, and/or silicon carbide, preferably SiC, and/or silicon oxynitrides.
 11. A composite structure according to claim 8, wherein said protective layer (3) comprises aluminum nitride, preferably AlN, and/or aluminum oxide, preferably Al₂O₃.
 12. A composite structure according to claim 8, wherein at least a plurality of metallic function layers, in particular strip conductors are at least disposed regionwise within said diamond layer (4) and/or at least are covered regionwise thereby.
 13. A composite structure according to claims 8, wherein all the surface regions of said component layer (2) which come into contact with the precursor material of said diamond layer (4) are covered with said protective layer (3).
 14. A composite structure according to one of the claims 8 to 13, wherein the layer thickness of said protective layer (3) has a value with which a thermal quality factor of said diamond and protective layer (3,4) of 1.5 or more is achieved. 